Boilers that are produced to be fitted outdoors are identified with a symbol that describes the extent to which their electrical parts are protected against environmental conditions such as humidity, dust particles, and others.
The acronym IP stands for "Ingress Protection".
There are two numbers after the initials IP. The first, from 1 to 6, indicates how hermetic the doors of the electrical panel are against the entry of dust. 6 is the degree that most outdoor appliances have, and this guarantees that the equipment is totally hermetically sealed against dust and particles even with a continuous air flow, as will be the case in an outdoor installation.
The second number shows the degree of protection against moisture.
Boilers are usually manufactured between the IP65 to IP68 ratings. 5 is a degree of protection against directed jets of water at low pressure, and 8 is for equipment operating submerged at great depth. The higher the level of humidity it can withstand, the higher the value of this rating.